Evolution (PCB 4674). Chapter 2. The evidence for evolution

EVOLUTION/LECTURE1 

Evolution (PCB 4674). 

Chapter 2. The evidence for evolution 

Main topics of lecture: 

I: The three main statements of the Theory of Special Creation 

1.- Introduction 

2.- Relatedness of life forms 

3.- Change through time 

4.- The age of the Earth 

II: Correspondence among data sets and Theory of Evolution 

I: General background: 

1.- Introduction 

1.1.- Before the establishment of the Theory of Evolution by Charles Darwin the leading 

explanation in Europe for the origin of species was the Theory of Special Creation. This 

theory held that all organisms were created by God during the six days of creation as 

described in the Bible's book of Genesis. The theory stated that species are unchanged since 

their creation, or immutable, and that variation within each species is strictly limited. 

1.2.- The Theory of Special Creation also stated that creation of all the organisms was recent 

(approx. 6,000 years ago). 

1.3.- By the time that Darwin began working with his theory dissatisfaction with the Theory 

of Special Creation had begun to grow. Research in the biological and geological sciences 

was advancing rapidly, and the data clashed with creationism's central tenets and predictions. 

1.4.- Scientific theories frequently have two components: 

(i) A statement of a fact: A claim about a pattern that exists in the natural world 

(ii) Which process is responsible for this patter 

1.5.- The three main statements of facts made by the Theory of Special Creation are: 

(i) Species were created independently of one another 

(ii) Species do not change through time 

(iii) Species were created recently 

1.6.- According to the Theory of Special Creation the process responsible for this pattern 

was the creation by God 

1.7.- In this chapter we will review evidence that supports an alternative statement: 

file:///E|/CH2-EVIDENCE-SPRING-2008/CHAPTER2_SPR_2008.HTML[12/8/2011 11:22:00 AM]


"Species have changed through time and are related by descent from a 

common ancestor" 

This statement is the backbone of the theory of evolution as exposed by Charles Darwin. 

1.8. In this chapter we will explore first data that challenges the three main statements of 

the Theory of Special Creation indicated in 1.5 (i.e. species are independent, immutable 

and recent). In the second half of the chapter we will introduce several data drawn from 

different fields of scientific inquiry that supports predictions of the Theory of Evolution 

2.- Relatedness of life forms and homology 

2.1.- The Theory of Special Creation contends that each species was created 

independently. In contrast the Theory of Evolution contends that organisms are related by 

common ancestry. 

2.2.- Results from the fields of comparative anatomy and embryology demonstrate that 

fundamental similarities underlie the obvious physical differences among species. Early 

researchers called this phenomenon homology. Two good examples can be found in the 

vertebrate skeletons and in flower organs. If species share common ancestors they also 

should share many characters of their ancestors. Homologous characters reflect the common 

ancestry of species 

2.3.- Vertebrates forelimbs are used for different functions, but they ALL HAVE the same 

sequence and arrangement of bones. 

Figure 2.1.a.: Vertebrate homologous bones. Homologous bones 

are colored or shaded in the same way, and are labeled on the 

human arm 



2.4.- Likewise orchid flowers are diverse in size and shape, but are comprised of elements 

that are similar in structure and orientation (Fig 2.1.b) 

Figure 2.1.b.: Homology among flower elements of two orchid 

species 

2.5.- Homologies can also be found at developmental, structural and embryonic levels. For 

instance the amino acid sequences encoded by a gene involved in the development of the 

eye exhibits 90% similarities among vertebrate and invertebrate organisms (Fig. 2.2.a) 

Figure 2.2.a.: Genetic homologies: The amino acid sequences of 

a section called the homeodomain in a protein involved in the 

development of the eye. Dots indicate the same amino acid as 

the one above 

2.6.- Advances in molecular genetics have revealed other fundamental similarities among 

organisms. One of the most spectacular is the genetic code. With a few minor exceptions, all 

organisms studied to date use the same nucleotide triplets, or codons, to specify the 

same amino-acid-bearing RNAs (Figure 2.2.b). 

Figure 2.2.b.: Genetic homologies: The genetic code; in almost 

every organism studied, the same nucleotide triplets, or codons, 

specify the same amino acid bearing transfer RNAs 



2.7.- Homology may appear to be an abstract concept. However, the concept of homology 

is the guiding principle behind most biomedical research. Homology is the reason medical 

researchers can obtain valid results when testing the safety of new drugs in rats. Results of 

these tests can be extrapolated to humans if the molecular or cellular basis of the phenomenon 

being studied is homologous. 

2.8.- Homology and Bio-Medical Research.- Bio-medical researchers choose a study 

organism - also called a "model" organism - based on the degree of homology required 

to study a particular process or disease. In psychiatry and the behavioral sciences, 

for example, monkeys and apes are often the preferred experimental subject 

because aspects of their behavior and brain structures are homologous with 

those of humans. Because some of the genes involved in more basic processes, like 

the cell cycle, are homologous between even distant relatives, researchers can use 

baker's yeast (Saccaromyces cerevisiae) to study why certain malfunctioning genes 

cause cancer in humans. At an even more fundamental level, the genes involved in 

DNA repair are homologous between humans and the bacterium Escherichia coli. 

Primates, yeast, and bacteria share these characteristics with humans because they 

inherited them from a common ancestor 

3.- Change through time 

3.1.- The second major statement of the Theory of Special Creation is that Species do not 

change through time. Evidence from living species and the fossil record challenge this 

view 

3.2.- Evidence from living species.- The existence of vestigial structures and direct 



observation of change of living species support the hypothesis that species change through 

time. 

3.3.- A Vestigial structure is a functionless rudimentary homologue of a body part that 

has a function in closely related species. For instance some blind, cave-dwelling creatures 

have eye sockets but no eyes, humans have a reduced tailbone, called the coccyx at the 

base of their vertebral column (Figs 2.3.a and 2.3.b) 

Figure 2.3.a.: Rudimentary tailbone of humans 

Figure 2.3.b.: The grotto salamander (Typhlotriton spelaeus) 

have functionless bulbs of tissue in place of eyes 



3.4.- Another example of a Vestigial structure can be found during the development 

of the "hands" (wing tips) and feet of birds. Adult chickens have three digits in their wings 

and four in their feet. But when chicken embryos are treated with a stain to mark the 

tissues that initiate bone development, and additional digit appears (in the wing and foot), 

and later disappears (Fig. 2.4). Most living and fossil tetrapods have five digits in their 

forelimbs and hindlimbs. It is logical, then, to argue that the ancestors of birds also had 

five digits in each limb 

Figure 2.4.: Adult chickens have three digits in their wings 

and four in their feet. But during development, an extra digit 

appears fort a short time in the hands and foot 

3.5.- Change through time can also be observed directly. Over the past 60 years, biologists 

have documented change in hundreds of different species!!!!. An example can 

be found in the soapberry bug in Florida. In the first part of the 20 th century, soapberry 

bugs [Jadera haematoloma (Hemiptera)] that were collected in Florida tended to have 

extremely long beaks. These insects feed on seeds that are located within the fruits at 

varyring distances from the fruit perimeter. At that time the most important 

host plant for the bugs was the Florida native large-fruited balloon vine 

[Cardiospermum corindum (Sapindaceae), Fig. 2.5.c; Sapindaceae is the plant family 

of the litchi tree]. In the mid 20 th century however, most populations of soapberry bugs 

began feeding on the small fruits of a plant that had just been imported from Asia as an 

ornamental species, called the flat-potted golden rain tree [Koelreuteria elegans (Sapindaceae), 

Fig. 2.5.d]. Soapberry bugs collected after the host-plant switch tend to have much smaller 

beaks than older populations (Figs. 2.5.a and 2.5.b) 



Figure 2.5.a.: Soapberry bugs feeding on the fruit of a balloon 

vine and a flat-podded golden tree 

Figure 2.5.b.: The scatterplot shows the beak lengths of female 

soapberry bugs from Florida in a 100 year period 



Figure 2.5.c.: Balloon vine[Cardiospermum corindum (Sapindaceae)]. 

Soapberry bugs from Florida fed mostly on fruits of this vine until 

the introduction of the golden rain tree (Koelreuteria elegans 

(Sapindaceae) 



Figure 2.5.d.: Golden rain tree (Koelreuteria elegans 

(Sapindaceae) 

3.6.- Evidence from the fossil record.- A fossil is a trace of any organism that lived in 

the past. The total, worldwide collection of fossils, scattered among thousands of different 

institutions and individuals, is called the fossil record. The simple fact that fossils exist, 

and that the vast majority of fossils forms are unlike species that are living today, argues 

that life has changed though time 

3.7.- The law of succession. There is a general correspondence between fossils and living 

forms. The law of succession maintains that the fossil species found in a giving area are 

usually succeeded by similar living species of this area. For instance the extinct marsupial 



fauna of Australia has a close relationship to marsupials alive today in this region. 

Likewise Darwin analyzed the armadillos of Argentina and their close glyptodons he 

excavated there (Fig. 2.9). Glyptodons went extinct around 10,000 years ago during the 

last ice age, after having lived in both North and South America 

Figure 2.9.: Early researchers observed close relationships 

between fossil and extant species from the same geographical 

area, and between fossil forms in adjacent rock strata, so 

routinely that the pattern became known as the law of 

succession. Darwin noted the similarities between the 

contemporary pygmy armadillo (Zaedyus pichiy) and the 

fossil of the giant glyptodont in Argentina 

3.8.- Transitional forms. Darwin maintained that species have changed through time, 

and that fossils represent populations that are ancestral to species alive today. If this 

is true, then the fossil record should contain forms that are transitional between 



major groups of organisms. These transitional species should have characteristics from 

the ancestral population as well as novel traits in descendant species. One of the 

best known examples is the most ancient bird in the fossil record, Archaeopteryx. 

The presence of feathers clearly identifies this species as a bird, but the skeleton 

is dinosaur-like. Archaeopteryxrepresents a transition between ancestral dinosaurs 

and their descendant, the birds (See Figure below). The oldest fossil of 

Archaeopteryxis is estimated to be 150 million years old. Because few transitional 

forms had been discovered in his lifetime, Darwin took pains to explain that they 

should be rare in the fossil record in a section os his book titled "Difficulties on 

Theory". In the intervening years, however a LARGE NUMBER OF 

TRANSITIONAL FORMS have been found 

3.9.- Environmental Change. Fossils of marine organisms have been discovered 



in the Andes in South America, the Alps of Europe, and the Grand Canyon of 

America's arid southwest. These observations suggest that the Earth itself has changed 

over time. Habitats have changed in location and character throughout the course of 

history. Landforms and habitats are continuously being modified, just as species are 

4.- The age of the Earth 

4.1.- The Theory of Special Creation establishes that the Earth is about 6,000 years old. 

However by the time of Darwin geological evidence was mounting that the Earth was 

much older. 

4.2.- Using the technique of relative dating geologists have established the chronology of 

relative dates known as the geologic time scale (Fig. 2.11). They also created the concept 

of the geological column, which is a geologic history of the Earth based on a composite, 

older-to-younger sequence of rock strata. Geologists began working in time scales of millions 

of years, instead of a few thousand years 

Figure 2.11.: The geological time scale. The sequence of eons, 

eras, periods, and epochs shown on the left part of this diagram 

was established through the techniques of relative dating. Each 

named interval of time is associated with a distinctive fossil flora 

and fauna. The absolute ages included here were added much later, 

when radiometric dating system became available. The abbreviation 

Ma stands for millions of years ago 



4.3.- Using a technique called radiometric dating, physicists and geologists began to assign 

absolute dates to the relative dates established by the geologic timer scale. The technique for 

radiometric dating utilizes unstable isotopes of naturally occurring elements. These radioactive 

isotopes (parent isotope) decay, meaning that they change into either different elements or 

different isotopes of the same element (daughter isotope). Each isotope decays at a particular 

and constant rate. These rates are not affected by temperature, moisture, or any other 

environmental factor. Researchers measure the ratio of parent isotope to daughter isotope 

in a rock sample. As a result, radioactive isotopes function as natural clocks. because of 

their slow decay rate potassium-argon and uranium-lead systems are the isotopes of choice 

for determining the age of the Earth (Fig. 2.12). 

4.4.- The oldest fossil organism discovered to date are impressions of bacterial cells found 

in 3.5 billion-year-old rocks from Western Australia. The oldest chemical evidence (carbon 

granules) of life is in rocks from Greenland dating more than 3.7. billion years old. It is 

estimated that the planet is about 4.6 billion years old. These data suggest that the Earth was 

lifeless for about 900 million years, and that evolution has been occurring for about 

3.7 billion years. 



II: Correspondence among data sets and Theory of Evolution 

5.1.- The data reviewed in this chapter contradict the proposition that species were 

created independently, that species are immutable, and that the Earth is young. These 

data are easily explained by the theory of evolution. There is another type of data 

that also supports the theory of evolution. This is a correspondence among independent 

sources of data on Earth history and the history of life. Geologists interpret Earth history 

through the Theory of Plate Tectonics. This theory contends that the Earth's crust is 

broken into plates and that the positions of these plates have change through time. When 

the geological data are combined with radiometric dates and data from the fossil record, 

a coherent picture of change through time emerges.

Evolution (PCB 4674). Chapter 2. The evidence for evolution

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